INTERACTION BETWEEN PROPAGATION SPEED AND FLAME STRUCTURE IN DOWNWARD CELLULAR PROPAGATING FLAME IN A COMBUSTION TUBE WITH CO_2 LASER IRRADIATION

摘要

This study investigates a downward propagating cellular flame to describe its transient phenomena induced by CO_2 laser irradiation. An experimental investigation has been conducted in a combustion tube with C_2H_4 - O_2 - CO_2 fuel rich mixtures at ambient temperature and atmospheric pressure. After ignition, a cellular flame is formed, and once CO_2 laser irradiates the mixture, several motions can be observed. First, transition from cellular to smooth surface occurs as a consequence of the local increment of the flame speed. Then, as the laser is continuously irradiating, concave structure develops and finally new cells appear around this concave structure because buoyancy overcomes the initial enhancement of the propagation speed, decelerating it close to the initial value where cellular flame can exist. Therefore, it is concluded that CO_2 laser actively controls the evolution of the propagating flame shape.